This invention relates to motorized vehicle control systems and more particularly to an electromic control system especially suited for electrically powered wheelchairs for use by disabled persons with severely limited ability to manipulate the limbs, particularly the hands and digits.
It has been found that disabled persons suffering from poor coordination, inadequate muscle strength or limited movement of the arms, hands and fingers, conditions which typically result from the afflictions of muscular dystrophy and multiple sclerosis, are largely unable to exercise the necessary degree of control for existing electrically powered wheelchairs. Presently available electrically-powered wheelchairs typically employ for control purposes either "ON-OFF" switch controls, a control stick associated with a plurality of electrical switches, or a rather crude proportional control system. Each of these systems suffers from serious disadvantages to be presently described.
The "ON-OFF" switch control system which usually employs either a manually actuable push-button switch or a mercury switch mounted on a headband results in an erratic and jerking vehicular motion due to the sudden starting and stopping of the electric motor which powers the wheelchair. Moreover, a sudden start of the wheelchair in one direction will cause the rider's head and body to jerk in the reverse direction, which in turn creates a sharp false instruction to the motor to reverse direction. Such rapid forward and reversing motions of the wheelchair causes it to wheel around rapidly out of control of the rider. A high degree of coordination of the upper body and neck of the rider is required to avoid or minimize the aforementioned loss of vehicle control but most disabled wheelchair riders lack the required muscular control to overcome the just-described oscillatory motion of the vehicle. Where digitally actuated push-button switches are employed, severely disabled riders find it very difficult to accurately position their hands and fingers over the various push-buttons, usually four in number, and apply sufficient pressure thereto in order to achieve the desired vehicular motion. On the other hand, the push-buttons may easily be accidentally actuated by an inadvertent brush of the finger, causing unwanted vehicular motion.
In the switch and control stick system, at least four switches and a control stick are provided. In order to achieve forward vehicular motion the rider moves the control stick forwardly to actuate the two forward switches, which concurrently cause the electric drive motor to rotate each wheel at equal speed in the forward direction.
Movement of the control stick to the right will cause actuation of the left front switch, causing the motor to rotate the left wheel forwardly, and actuation of the right rear switch causing the motor to rotate the right wheel in reverse, thus causing the wheelchair to pivot to the right. Again, due to the "ON-OFF" nature of the four switches, sudden changes in vehicular motion result, particularly if the motor speed controls are set to the High Speed position, as is usually the case. Unfortunately, due to their muscular disabilities, many such persons confined to a wheelchair find themselves unable to exercise a sufficient degree of control over the vehicle. Even if the control stick is moved straight ahead, due to positional inaccuracies of the two forward switches they will not actuate perfectly simultaneously, whereby the wheelchair moves slightly to the left or right before moving forwardly. In addition, due to differences in friction or electrical wiring of the left and right drive motors, the wheelchair will tend to "wander" to the right or left requiring steering correction by the rider.
The use of switch controls imposes a severe reduction of battery life due to the fact that maximum power is always applied to the wheel drive motors on start-up even if the wheelchair is to be moved a short distance.
In presently available proportional control systems, which avoid some of the above-described problems in "ON-OFF" switching systems, the motor speed, i.e., wheel velocity is determined by the magnitude of the displacement of the control stick from its rest position. Motor speed control is achieved by varying the motor current by means of a variable resistor which is heavy, bulky and is very wasteful of battery-supplied electrical power due to the large amount of electrical power and resultant heat which must be dissipated. Where such motor speed control is accomplished by means of transistor or gate controlled rectifier switching circuitry, the required relays and other control circuitry greatly increases both the size and cost of the overall control system.
It is therefore an object of the present invention to provide an electronic control system for controlling electromotive apparatus which avoids the above-described deficiencies in existing control systems.
It is another object of the present invention to provide an electronic control system of the character described which is reliably operative in a severe mechanical and electrical environment.
It is a further object of the present invention to provide an electronic control system of the character described which is remotely operated by human touch.
It is yet another object of the present invention to provide an electronic control system of the character described which is particularly adapted for use by disabled persons in driving and steering a wheelchair.